Subsystem: Myxoxanthophyll biosynthesis in Cyanobacteria

This subsystem's description is:

The pathway for synthesis of Myxoxanthophyll (myxol-2' fucoside), a glycosylated carotenoid found uniquely in members of the phylum Cyanobacteria.

The glycosylated carotenoids of cyanobacteria are unique in that glycosylation characteristically occurs on the C-2'-hydroxyl group rather than that at the C-1' position of the {psi} end of myxol (3',4'-didehydro-1',2'-dihydro-β,{psi}-carotene-3,1',2'-triol) or oscillol (3,4,3',4'-tetradehydro-1,2,1',2'-{psi},{psi}-carotene-1,2,1',2'-tetrol) to form myxoxanthophyll or oscillaxanthin, respectively.

Myxoxanthophyll is synthesized from lycopene, the acyclic precursor of all carotenoids in cyanobacteria.

The first committed step in myxol-2' fucoside synthesis is the hydroxylation of the tertiary carbon of a {psi} end of lycopene or {gamma}-carotene by CruF. This hydroxylation reaction would sequester the intermediate product from the pool of substrate molecules available to the CruA and CruP lycopene cyclases. The formation of the β-ionone ring by lycopene cyclase either before or after hydroxylation would lead to 1'-hydroxy-{gamma}-carotene. This compound would next be converted into 3-dehydroxymyxol (plectaniaxanthin) by an as-yet-unidentified enzyme(s). Finally, CruG glycosylates the hydroxyl group at the 2' position to form myxoxanthophyll.

See Illustration.

CruF is the C-1'-hydroxylase
CruA is a lycopene cyclase
The well-conserved β-hydroxylase CrtR functions in the C-3 hydroxylation of myxoxanthophyll
CruG is the 2'-O-glycosyltransferase

CruF and CruG are uniquely required for mxyoxanthophyll biosynthesis.

For more information, please check out the description and the additional notes tabs, below

Literature ReferencesThe biosynthetic pathway for myxol-2' fucoside (myxoxanthophyll) in the cyanobacterium Synechococcus sp. strain PCC 7002. Graham JE Journal of bacteriology 2009 May19304845
DiagramFunctional RolesSubsystem SpreadsheetDescriptionAdditional Notes 
Group Alias
Abbrev.Functional RoleReactionsScenario ReactionsGOLiterature
SubsetsColoring
collapsed
expanded


  
display  items per page
«first  «prevdisplaying 1 - 119 of 119next»  last»
Taxonomy Pattern 
Organism 
Domain
Variant [?] 
active
CruFCruGCruACrtRCruPCrtL
«first  «prevdisplaying 1 - 119 of 119next»  last»
The pathway for synthesis of Myxoxanthophyll (myxol-2' fucoside), a glycosylated carotenoid found uniquely in members of the phylum Cyanobacteria.

The glycosylated carotenoids of cyanobacteria are unique in that glycosylation characteristically occurs on the C-2'-hydroxyl group rather than that at the C-1' position of the {psi} end of myxol (3',4'-didehydro-1',2'-dihydro-β,{psi}-carotene-3,1',2'-triol) or oscillol (3,4,3',4'-tetradehydro-1,2,1',2'-{psi},{psi}-carotene-1,2,1',2'-tetrol) to form myxoxanthophyll or oscillaxanthin, respectively.

Myxoxanthophyll is synthesized from lycopene, the acyclic precursor of all carotenoids in cyanobacteria.

The first committed step in myxol-2' fucoside synthesis is the hydroxylation of the tertiary carbon of a {psi} end of lycopene or {gamma}-carotene by CruF. This hydroxylation reaction would sequester the intermediate product from the pool of substrate molecules available to the CruA and CruP lycopene cyclases. The formation of the β-ionone ring by lycopene cyclase either before or after hydroxylation would lead to 1'-hydroxy-{gamma}-carotene. This compound would next be converted into 3-dehydroxymyxol (plectaniaxanthin) by an as-yet-unidentified enzyme(s). Finally, CruG glycosylates the hydroxyl group at the 2' position to form myxoxanthophyll.

See Illustration.

CruF is the C-1'-hydroxylase
CruA is a lycopene cyclase
The well-conserved β-hydroxylase CrtR functions in the C-3 hydroxylation of myxoxanthophyll
CruG is the 2'-O-glycosyltransferase

CruF and CruG are uniquely required for mxyoxanthophyll biosynthesis.
The CruA- and CruP- type lycopene cyclase

Maresca JA, Graham JE, Wu M, Eisen JA, Bryant DA. Identification of a fourth family of lycopene cyclases in photosynthetic bacteria. Proc Natl Acad Sci U S A. 2007 Jul 10;104(28):11784-9.
Abstract
A fourth and large family of lycopene cyclases was identified in photosynthetic prokaryotes. The first member of this family, encoded by the cruA gene of the green sulfur bacterium Chlorobium tepidum, was identified in a complementation assay with a lycopene-producing strain of Escherichia coli. Orthologs of cruA are found in all available green sulfur bacterial genomes and in all cyanobacterial genomes that lack genes encoding CrtL- or CrtY-type lycopene cyclases. The cyanobacterium Synechococcus sp. PCC 7002 has two homologs of CruA, denoted CruA and CruP, and both were shown to have lycopene cyclase activity. Although all characterized lycopene cyclases in plants are CrtL-type proteins, genes orthologous to cruP also occur in plant genomes. The CruA- and CruP-type carotenoid cyclases are members of the FixC dehydrogenase superfamily and are distantly related to CrtL- and CrtY-type lycopene cyclases. Identification of these cyclases fills a major gap in the carotenoid biosynthetic pathways of green sulfur bacteria and cyanobacteria.
PMID: 1760690